This paper presents a study on the performances of a group of planar monopoles using radiators of different shapes, such as triangle, rectangle, square, annual ring, circle, horizontal ellipse, vertical ellipse, pentagon, and hexagon, for ultra-wideband (UWB) bodycentric wireless communications. The planar monopoles have the radiators with microstrip-fed line printed on one side of the substrate and a ground plane on the other side. Simulation studies show that, among these monopoles, the horizontal elliptical, vertical elliptical, and hexagonal monopoles have better overall performances in terms of bandwidth, gain, efficiency, and radiation pattern in free space. A solid-body phantom mimicking human tissue is used for studies of these three monopoles for body-centric communications. Simulated and measured results of these monopoles on the phantom show that the horizontal elliptical monopole achieves the widest impedance bandwidths, highest average peak gain and efficiency, least path loss, best fidelity, and good radiation pattern, making it a good candidate for UWB body-centric wireless communications.

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An offset-fed ISM/Ultra-wideband (UWB) antenna with a slotted ground plane designed for on-body communications is presented in this paper. The antenna consists of a radiator very close to a square shape, a feed line slightly offset from the middle along the radiator side and three rectangular slots at the top edge of the ground plane. The offset feed line is used to improve the radiation pattern for on-body communications and the slots on the ground plane are used to improve impedance matching of the antenna. The antenna is studied using computer simulation. For verification of simulation results, the antenna is fabricated and measured. Simulated and measured results show good agreements in terms of reflection coefficient, gain, efficiency and radiation pattern. Measured results show that the antenna can achieve a wide bandwidth from 2.38 to 14.5 GHz with more omnidirectional radiation patterns in the E-plane than conventional monopole, making it a potential candidate for on-body communications using UWB.

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